CN107159700B - Method for removing arsenic in heavy metal contaminated soil - Google Patents
Method for removing arsenic in heavy metal contaminated soil Download PDFInfo
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- CN107159700B CN107159700B CN201710515001.3A CN201710515001A CN107159700B CN 107159700 B CN107159700 B CN 107159700B CN 201710515001 A CN201710515001 A CN 201710515001A CN 107159700 B CN107159700 B CN 107159700B
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- 229910052785 arsenic Inorganic materials 0.000 title claims abstract description 168
- 229910001385 heavy metal Inorganic materials 0.000 title claims abstract description 85
- 238000000034 method Methods 0.000 title claims abstract description 39
- 239000000706 filtrate Substances 0.000 claims abstract description 167
- 238000004090 dissolution Methods 0.000 claims abstract description 118
- 238000001179 sorption measurement Methods 0.000 claims abstract description 49
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 47
- 239000003623 enhancer Substances 0.000 claims abstract description 41
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 38
- 238000002156 mixing Methods 0.000 claims abstract description 34
- 239000003463 adsorbent Substances 0.000 claims abstract description 25
- 229910052742 iron Inorganic materials 0.000 claims abstract description 13
- 230000029087 digestion Effects 0.000 claims abstract description 8
- 238000010828 elution Methods 0.000 claims description 50
- 239000000243 solution Substances 0.000 claims description 25
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 20
- 229910020489 SiO3 Inorganic materials 0.000 claims description 18
- 239000007864 aqueous solution Substances 0.000 claims description 16
- 239000000203 mixture Substances 0.000 claims description 16
- 229910052911 sodium silicate Inorganic materials 0.000 claims description 16
- 229910017677 NH4H2 Inorganic materials 0.000 claims description 11
- 238000003756 stirring Methods 0.000 claims description 11
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 claims description 10
- 230000010355 oscillation Effects 0.000 claims description 8
- 239000012744 reinforcing agent Substances 0.000 claims description 7
- 239000003929 acidic solution Substances 0.000 claims description 6
- 239000003795 chemical substances by application Substances 0.000 claims description 6
- 238000005728 strengthening Methods 0.000 claims description 5
- 239000007836 KH2PO4 Substances 0.000 claims description 4
- 150000001875 compounds Chemical class 0.000 claims description 4
- 150000002500 ions Chemical class 0.000 claims description 4
- 229910000402 monopotassium phosphate Inorganic materials 0.000 claims description 4
- GNSKLFRGEWLPPA-UHFFFAOYSA-M potassium dihydrogen phosphate Chemical compound [K+].OP(O)([O-])=O GNSKLFRGEWLPPA-UHFFFAOYSA-M 0.000 claims description 4
- 229910052882 wollastonite Inorganic materials 0.000 claims description 4
- 238000010521 absorption reaction Methods 0.000 abstract description 4
- 230000008569 process Effects 0.000 abstract description 4
- 230000002860 competitive effect Effects 0.000 abstract description 2
- 238000005067 remediation Methods 0.000 abstract description 2
- 238000000605 extraction Methods 0.000 abstract 1
- 238000011065 in-situ storage Methods 0.000 abstract 1
- 241000209094 Oryza Species 0.000 description 68
- 235000007164 Oryza sativa Nutrition 0.000 description 68
- 235000009566 rice Nutrition 0.000 description 68
- 229910019142 PO4 Inorganic materials 0.000 description 30
- 238000002386 leaching Methods 0.000 description 22
- 238000001914 filtration Methods 0.000 description 21
- 230000000052 comparative effect Effects 0.000 description 9
- 230000000694 effects Effects 0.000 description 9
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 6
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 5
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- 238000007254 oxidation reaction Methods 0.000 description 3
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- 238000006722 reduction reaction Methods 0.000 description 3
- 241000196324 Embryophyta Species 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000005034 decoration Methods 0.000 description 2
- 238000003795 desorption Methods 0.000 description 2
- 238000009393 electroremediation Methods 0.000 description 2
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- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 2
- 239000010452 phosphate Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000007873 sieving Methods 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- DJHGAFSJWGLOIV-UHFFFAOYSA-K Arsenate3- Chemical compound [O-][As]([O-])([O-])=O DJHGAFSJWGLOIV-UHFFFAOYSA-K 0.000 description 1
- 229910017251 AsO4 Inorganic materials 0.000 description 1
- 206010005003 Bladder cancer Diseases 0.000 description 1
- 229910003243 Na2SiO3·9H2O Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 208000000453 Skin Neoplasms Diseases 0.000 description 1
- 208000007097 Urinary Bladder Neoplasms Diseases 0.000 description 1
- UJGOCJFDDHOGRX-UHFFFAOYSA-M [Fe]O Chemical compound [Fe]O UJGOCJFDDHOGRX-UHFFFAOYSA-M 0.000 description 1
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- 230000002378 acidificating effect Effects 0.000 description 1
- 230000009471 action Effects 0.000 description 1
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- 125000000129 anionic group Chemical group 0.000 description 1
- 150000001450 anions Chemical class 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 229940000489 arsenate Drugs 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000000711 cancerogenic effect Effects 0.000 description 1
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- 229910052909 inorganic silicate Inorganic materials 0.000 description 1
- 201000007270 liver cancer Diseases 0.000 description 1
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- 230000003211 malignant effect Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
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- 229910052751 metal Inorganic materials 0.000 description 1
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- 125000000896 monocarboxylic acid group Chemical group 0.000 description 1
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- 238000003199 nucleic acid amplification method Methods 0.000 description 1
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- RMAQACBXLXPBSY-UHFFFAOYSA-N silicic acid Chemical compound O[Si](O)(O)O RMAQACBXLXPBSY-UHFFFAOYSA-N 0.000 description 1
- 235000012239 silicon dioxide Nutrition 0.000 description 1
- 201000000849 skin cancer Diseases 0.000 description 1
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/02—Extraction using liquids, e.g. washing, leaching, flotation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/08—Reclamation of contaminated soil chemically
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Soil Sciences (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Processing Of Solid Wastes (AREA)
Abstract
The invention provides a method for removing arsenic in heavy metal contaminated soil, which comprises the steps of mixing a reinforcer, water and heavy metal soil, and then carrying out dissolution treatment on the arsenic contaminated soil to obtain dissolution filtrate; and then adsorbing the digestion filtrate by using an iron-based adsorbent. The invention can realize the enhanced dissolution of arsenic in heavy metal contaminated soil by adopting the enhancer, can quickly realize the combination with the dissolved arsenic by combining the adsorption of a subsequent adsorbent, realizes the absorption and removal of arsenic, and can realize the efficient and thorough removal of arsenic in soil by combining the in-situ competitive release process and the ectopic adsorption extraction process in the remediation, thereby avoiding secondary pollution. The results of the embodiment show that the arsenic removal rate of the arsenic-containing soil treated according to the technical scheme provided by the invention reaches 27-31%.
Description
Technical Field
The invention belongs to the technical field of environmental management, and particularly relates to a method for removing arsenic in heavy metal contaminated soil.
Background
As has become the leading highly toxic metal causing large-area pollution of water, soil and rice in China, and is classified As a known carcinogen by the World Health Organization (WHO) and the Environmental Protection Agency (EPA). The arsenic pollution of the soil has the characteristics of concealment, irreversibility, long-term property and the like, the arsenic pollution not only affects the soil fertility, the crop yield and the quality, but also can cause malignant diseases such as skin cancer, bladder cancer, liver cancer and the like when biological organisms contact the arsenic for a long time through the biological amplification effect of a food chain.
The current methods for removing As from soil include: phytoremediation, soil leaching, a soil-visiting method and electrokinetic remediation, wherein the phytoremediation method can remove the As in the rice soil from the soil, but has long remediation time, great influence by the climate environment and low removal rate; the soil leaching method and the soil dressing method have large engineering quantity and high cost, and can cause low removal rate of As; the electrokinetic remediation method must be carried out under acidic conditions, and also has a problem of low removal rate.
Disclosure of Invention
In view of the above, the present invention provides a method for removing arsenic from heavy metal contaminated soil, which has a high removal rate and can avoid secondary pollution.
In order to achieve the above object, the present invention provides the following technical solutions:
A method for removing arsenic in heavy metal contaminated soil comprises the following steps:
(1) Mixing the reinforcer, the heavy metal contaminated soil and water, and then carrying out arsenic dissolution treatment on the heavy metal contaminated soil to obtain dissolution filtrate;
(2) And adsorbing the digestion filtrate by using an iron-based adsorbent.
Preferably, the arsenic elution treatment is oscillation elution or stirring elution; the frequency of the shaking elution and the stirring elution are independently 150 to 200 rpm.
Preferably, the iron-based adsorbent in step (2) is zero-valent iron or iron oxide.
Preferably, the amount of the water is measured by the height exceeding the surface of the heavy metal polluted soil, and the height exceeding the surface of the heavy metal polluted soil is 2-5 cm.
Preferably, the enhancer is NH4 +、H2PO4 -、HPO4 2-、C2O4 2-And SiO3 2-A compound or mixture of one or more ions.
Preferably, the fortifier comprises NH4H2PO4、(NH4)2C2O4、Na2SiO3、KH2PO4、 Na2C2O4And CaSiO3One or more of (a).
Preferably, the mass of the enhancer is 7-21% of the mass of the heavy metal contaminated soil.
preferably, when the fortifier comprises NH4H2PO4、(NH4)2C2O4And Na2SiO3When is in contact with the NH4H2PO4The mass of the heavy metal-contaminated soil is 5-10% of the mass of the heavy metal-contaminated soil; said (NH)4)2C2O4The mass of the heavy metal-contaminated soil is 20-50% of the mass of the heavy metal-contaminated soil; the Na is2SiO3The mass of the heavy metal-contaminated soil is 15-30% of the mass of the heavy metal-contaminated soil.
Preferably, when the enhancer contains SiO3 2-And adjusting the pH value of the dissolution filtrate before adsorption, specifically, adjusting the pH value of the dissolution filtrate to 6.9-7.1 by using an acidic solution.
Preferably, the mass ratio of the adsorbent to the volume of the dissolution filtrate is 1-4 g: 1L.
The invention provides a method for removing arsenic in heavy metal contaminated soil, which comprises the steps of mixing a reinforcer, water and heavy metal soil, and then carrying out dissolution treatment on the heavy metal contaminated soil to obtain dissolution filtrate; and then adsorbing the digestion filtrate by using an iron-based adsorbent. The invention can realize the dissolution of arsenic in heavy metal polluted soil by adopting the enhancer, can quickly realize the combination with the dissolved arsenic by combining the subsequent coordination complexing, reduction and oxidation adsorption action mechanisms of the iron-based adsorbent to the arsenic, realizes the absorption of the arsenic, reduces the toxicity and avoids secondary pollution. The results of the embodiment show that the arsenic removal rate of the arsenic-containing soil treated according to the technical scheme provided by the invention reaches 27-31%.
Detailed Description
The invention provides a method for removing arsenic in heavy metal contaminated soil, which comprises the steps of mixing a reinforcer, heavy metal contaminated soil and water, and then carrying out arsenic dissolution treatment on the heavy metal contaminated soil to obtain dissolution filtrate; and then adsorbing the digestion filtrate by using an iron-based adsorbent.
According to the invention, the enhancer is adopted to realize the dissolution of arsenic in the heavy metal contaminated soil, the subsequent iron-based adsorbent is combined to play the triple functions of adsorption, reduction and oxidation, the dissolution of arsenic can be quickly realized, the arsenic in the filtrate can be thoroughly removed, the toxicity is reduced, and the secondary pollution is avoided.
In the invention, the heavy metal contaminated soil to be repaired is arsenic contaminated soil; the content of arsenic in the heavy metal contaminated soil can be 10-100.0 mg/kg. In the embodiment of the invention, the heavy metal contaminated soil is specifically rice soil with arsenic content of 20mg/kg, 40mg/kg, 60.43mg/kg or 80 mg/kg. The invention has no special requirements on the source of the heavy metal contaminated soil, and can be obtained by adopting the method well known by the technical personnel in the field; in the embodiment of the invention, the heavy metal contaminated soil is specifically rice soil collected from a bay As contaminated by the royal county of Cili county, Hunan province, which is located at 110.96 ° of east longitude and 29.35 ° of northern latitude.
The invention mixes the intensifying agent, the heavy metal contaminated soil and water, and then carries out arsenic dissolving treatment on the heavy metal contaminated soil to obtain dissolving filtrate. In the present invention, the arsenic elution treatment is preferably shaking elution or stirring elution. In the present invention, the frequency of the shaking elution and the frequency of the stirring elution are independently preferably 150 to 200rpm, and more preferably 175 to 190 rpm. In the invention, the time for arsenic leaching treatment is preferably 12-60 h, and more preferably 15-40 h; in the embodiment of the present invention, the time of the arsenic elution treatment is specifically 16h, 20h, 24h, 30h, 32h, 45h, 48h, 50h or 55 h. The present invention does not require any special embodiment of the shaking and stirring dissolution, and a mixture shaking method or a stirring method known to those skilled in the art may be used. Preferably, arsenic is dissolved out in the process of mixing the enhancer, the heavy metal contaminated soil and water.
In the invention, the amount of the water is preferably calculated by the height exceeding the surface of the heavy metal contaminated soil, and the height exceeding the surface of the heavy metal contaminated soil is preferably 2-5 cm, and more preferably 2.5-3.5 cm.
In the present invention, the fortifier preferably comprises NH4 +、H2PO4 -、HPO4 2-、C2O4 2-And SiO3 2-A compound or mixture of one or more ions. In the present invention, the enhancer includes NH4H2PO4、(NH4)2C2O4、Na2SiO3、KH2PO4、Na2C2O4And CaSiO3One or more of (a). Invention for said NH4H2PO4、(NH4)2C2O4、Na2SiO3、KH2PO4、Na2C2O4And CaSiO3The specific source of (A) is not particularly required and may be any source known to those skilled in the art; in the inventionIn the examples, the NH4H2PO4、(NH4)2C2O4And Na2SiO3In particular NH4H2PO4、 (NH4)2C2O4And Na2SiO3Commercially available products of (1), e.g. the said Na2SiO3May be specifically Na2SiO3·9H2O。
In the present invention, phosphate radical (H)2PO4 -/HPO4 2-) With arsenate (H)2AsO4 -/HAsO4 2-) Are typical chemical analogues with oxygen-containing ions having very similar pKa and thermochemical radii, hence, phosphate (MPO)4) The composite material has highly consistent competitive desorption effect on soil solid phase As (V) and obvious inhibition effect on re-adsorption of As (V), can remarkably improve the concentration of water-soluble As in soil, and is convenient for subsequent adsorption of water-soluble arsenic by C-NZVI, thereby improving the removal rate of arsenic in soil.
In the present invention, (NH)4)2C2O4The addition of the element (A) can lead the soil to be in amorphous and weak crystalline hydrated iron-aluminum oxide bonding state As to be resolved; the subsequent adsorption of the iron-based adsorbent to water-soluble arsenic is facilitated, so that the removal rate of arsenic in soil is improved.
In the present invention, silicic acid (H)4SiO4pKa 9.8, molecular diameter) With reduced As (III) (H)3AsO3pKa 9.2, molecular diameter) Are typical chemical analogs. Under the flooding condition, the addition of the enhancer containing the silicate radicals into the soil is favorable for desorption and release of the adsorption As (III) into the water phase of the soil, and is also convenient for the subsequent adsorption of C-NZVI on water-soluble arsenic, so that the removal rate of the arsenic in the soil is improved.
In the invention, the mass of the enhancer is 60-700 mg/kg, more preferably 65-663.54 mg/kg, and even more preferably 75.67-449.64 mg/kg of the mass of the heavy metal contaminated soil.
When the enhancer comprises NH4H2PO4、(NH4)2C2O4And Na2SiO3When is in contact with the NH4H2PO4The mass of the heavy metal-contaminated soil is preferably 60-80 mg/kg, and more preferably 65-75.67 mg/kg; said (NH)4)2C2O4The mass of the heavy metal-polluted soil is preferably 360-390 mg/kg, and more preferably 373.97-380 mg/kg; the Na is2SiO3The mass of (b) is preferably 200-230 mg/kg, and more preferably 213.9-220 mg/kg of the mass of the heavy metal contaminated soil.
In the present invention, the arsenic leaching treatment of the heavy metal contaminated soil is preferably performed by mixing a strengthening agent and water to obtain a strengthening agent aqueous solution, and then performing a leaching treatment of the heavy metal contaminated soil with the strengthening agent aqueous solution to obtain a leaching filtrate. The mixing mode of the enhancer and water is not particularly required, and the solution mixing mode which is well known to those skilled in the art can be adopted. In the present invention, the usage amounts of the enhancer and water are the same as those of the enhancer and water in the above technical scheme, and are not described herein again.
In the present invention, the arsenic elution treatment is preferably shaking elution or stirring elution; the frequency of the oscillation elution and the stirring elution is preferably 150 to 200rpm independently, and more preferably 160 to 180 rpm; the time of the oscillation elution and the stirring elution are independently preferably 12 to 20 hours, and more preferably 15 to 16 hours. In the invention, the time of the dissolution treatment ensures that the enhancer is fully contacted with the soil to be treated, thereby facilitating the dissolution of arsenic in the soil; when the enhancer is used for dissolution treatment step by step, the dissolution treatment time in each step of dissolution treatment process is preferably 12-20 h independently, and more preferably 15-16 h. For example, a certain amount of enhancer is adopted to realize enhanced dissolution of the soil to be treated within 16 h; when the reinforcing agent is subjected to reinforced dissolution in three steps, the reinforced dissolution time of each step is 16 hours.
In the invention, it is preferable that the heavy metal contaminated soil is subjected to arsenic leaching treatment, and the heavy metal contaminated soil is mixed with water to be subjected to flooding treatment, the enhancer is added to the flooded heavy metal contaminated soil, and the heavy metal contaminated soil is subjected to leaching treatment to obtain leaching filtrate. In the present invention, the usage amounts of the enhancer and water are the same as those of the enhancer and water in the above technical scheme, and are not described herein again. In the invention, the flooding treatment is preferably carried out by mixing the heavy metal contaminated soil with water, preferably adding water into the heavy metal contaminated soil, and the invention has no special requirement on the adding mode of the water and can adopt the method which is well known by the technical personnel in the field. In the invention, the time of the flooding treatment is preferably 6-10 days.
In the present invention, the dissolution treatment is the same as the dissolution treatment described in the above technical solution, and details thereof are not repeated herein.
In the present invention, the elution treatment is preferably two-step elution. In the present invention, the two-step dissolution preferably comprises: mixing the heavy metal contaminated soil, water and a part of the reinforcer, and carrying out primary dissolution on the heavy metal contaminated soil to obtain primary dissolution filtrate and secondary heavy metal contaminated soil; and carrying out secondary dissolution on the second heavy metal contaminated soil by adopting the residual enhancer and water to obtain a second dissolution filtrate. In the invention, the mass ratio of the partial enhancer and the residual enhancer has no special requirement; in the embodiment of the invention, the mass ratio of the partial reinforcing agent to the residual reinforcing agent is preferably 1 (4.87-6), more preferably 1 (4.93-5.84), and still more preferably 1: 5.15.
In the present invention, the time for the first elution is preferably 12 to 20 hours, and more preferably 16 hours. In the present invention, the requirement of the first dissolution is consistent with the requirement of the dissolution treatment described in the above technical scheme, and details are not repeated herein. After the mixture after the first dissolution is obtained, the invention preferably performs centrifugal filtration on the mixture after the first dissolution to obtain a first dissolution filtrate and second heavy metal contaminated soil. In the invention, the rotation speed of centrifugal filtration is preferably 3000-3500 r/min, and the time of centrifugal filtration is preferably 5-10 min. The present invention does not require any particular embodiment of the centrifugal filtration, and can be implemented by those skilled in the art.
The present invention preferably uses said (NH)4)2C2O4The obtained second heavy metal contaminated soil is subjected to second dissolution by the aqueous solution to obtain second dissolution filtrate. In the present invention, the time for the second elution is preferably 12 to 20 hours, and more preferably 16 hours. In the present invention, the requirement of the second dissolution is the same as the requirement of the dissolution treatment described in the above technical solution, and details are not repeated here. After the mixture after the second dissolution is obtained, the present invention preferably performs centrifugal filtration on the mixture after the second dissolution to obtain a second dissolution filtrate. In the invention, the rotation speed of centrifugal filtration is preferably 3000-3500 r/min, and the time of centrifugal filtration is preferably 5-10 min. The present invention does not require any particular method for carrying out the centrifugal filtration, and can be carried out by a centrifugal filtration method known to those skilled in the art.
The present invention uses a mixed filtrate of the first dissolution filtrate and the second dissolution filtrate as a dissolution filtrate for subsequent adsorption.
in the present invention, when the fortifier comprises NH4H2PO4And (NH)4)2C2O4The two-step dissolution specifically comprises: with the use of said NH4H2PO4The water solution is used for carrying out primary dissolution on the heavy metal contaminated soil to obtain primary dissolution filtrate and secondary heavy metal contaminated soil; with the said (NH)4)2C2O4The second heavy metal contaminated soil is subjected to second dissolution by the aqueous solution to obtain a second dissolution filtrate.
In the present invention, the elution treatment is also preferably three-step elution. The three-step dissolution preferably comprises: mixing the heavy metal contaminated soil, water and a first portion of enhancer, and carrying out primary dissolution on the heavy metal contaminated soil to obtain primary dissolution filtrate and second heavy metal contaminated soil; mixing a second enhancer, water and second heavy metal contaminated soil, and performing second dissolution to obtain a second dissolution filtrate and third heavy metal contaminated soil; and mixing the third enhancer, water and the third heavy metal contaminated soil, and dissolving out for the third time.
The invention has no special requirement on the relative dosage of the first enhancer, the second enhancer and the third enhancer; in the embodiment of the invention, the mass ratio of the first enhancer, the second enhancer and the third enhancer is preferably 1 (4.87-6) to (2.82-3.38), and more preferably 1 (4.93-5.84) to (2.87-3.33).
The conditions of the first dissolution and the second dissolution are the same as those of the first dissolution and the second dissolution in the technical scheme, and are not described herein again.
In the present invention, it is preferable that the mixture after the second leaching is subjected to centrifugal filtration to obtain a second leaching filtrate and a third heavy metal-contaminated soil. The Na is preferably used in the present invention2SiO3The third leaching solution is carried out on the third heavy metal contaminated soil by the aqueous solution of (2) to obtain a third leaching filtrate. In the present invention, the time for the third elution is preferably 12 to 20 hours, and more preferably 16 hours. In the present invention, the third dissolution is consistent with the requirements of the dissolution treatment described in the above technical solution, and will not be described herein again. In the invention, the rotation speed of centrifugal filtration is preferably 3000-3500 r/min, and the time of centrifugal filtration is preferably 5-10 min. The present invention does not require any particular method for carrying out the centrifugal filtration, and can be carried out by a centrifugal filtration method known to those skilled in the art.
The method takes the mixed filtrate of the first dissolution filtrate, the second dissolution filtrate and the third dissolution filtrate after pH value adjustment as the dissolution filtrate for the subsequent adsorbent adsorption.
In the present invention, when the fortifier comprises NH4H2PO4、(NH4)2C2O4And Na2SiO3In the case of the three-step dissolutionThe method comprises the following steps: with the use of said NH4H2PO4The water solution is used for carrying out primary dissolution on the heavy metal contaminated soil to obtain primary dissolution filtrate and secondary heavy metal contaminated soil; with the said (NH)4)2C2O4The water solution is used for carrying out secondary dissolution on the second heavy metal contaminated soil to obtain a secondary dissolution filtrate and third heavy metal contaminated soil; with the use of said Na2SiO3The third leaching solution is carried out on the third heavy metal contaminated soil by the aqueous solution of (2) to obtain a third leaching filtrate.
In the present invention, it is preferable that the leaching treatment is performed before the heavy metal contaminated soil is pretreated. In the present invention, the pretreatment is preferably performed by removing impurities, grinding, sieving, and adjusting the water content in this order. The method has no special requirement on the impurity removal mode so as to remove the impurities in the soil; in the invention, the inclusions are specifically stones, plant branches and leaves or plant roots. After grinding, sieving by adopting a sieve with sieve holes of 2mm preferably; the water content of the obtained undersize is preferably adjusted to obtain the heavy metal contaminated soil with the water content of 5-10 wt%. The invention does not require special embodiments of the grinding, and the removal of the inclusions can be achieved by grinding means well known to those skilled in the art.
After the mixture subjected to the elution treatment is obtained, the present invention preferably performs centrifugal filtration on the mixture subjected to the shaking elution to obtain an elution filtrate. In the invention, the rotation speed of centrifugal filtration is preferably 3000-3500 r/min, and the time of centrifugal filtration is preferably 5-10 min. The present invention does not require any particular embodiment of the centrifugal filtration, and can be implemented by those skilled in the art.
After the digestion filtrate is obtained, the iron-based adsorbent is adopted to adsorb the digestion filtrate. In the invention, the mass-to-filtrate volume ratio of the iron-based adsorbent is preferably 1-4 g:1L, more preferably 1.5-3 g:1L of the compound. In the present invention, the iron-based adsorbent is preferably zero-valent iron or iron oxide.
When zero-valent iron is selected, the zero-valent iron is preferably nano zero-valent iron, and is further preferably chitosan-loaded nano zero-valent iron (C-NZVI). The invention has no special requirement on the source of the chitosan loaded nano zero-valent iron, and the chitosan loaded nano zero-valent iron which is well known by the technical personnel in the field can be adopted. In the invention, the chitosan loads Fe contained in nano zero-valent iron (C-NZVI)0The core part of the core-shell structure of the iron oxide or the hydroxyl iron is relatively dense zero-valent iron, plays triple functions of adsorption, reduction and oxidation, can be quickly combined with dissolved arsenic, realizes the absorption of the arsenic, reduces the toxicity and avoids secondary pollution.
When iron oxide is selected, the iron oxide is preferably Fe2O3. The source of the iron oxide is not particularly required in the present invention and may be any source known to those skilled in the art.
In the invention, the adsorption time is preferably 20-24 h.
When the enhancer contains SiO3 2-Preferably, the adjusting of the pH value of the dissolution filtrate is further included before the adsorption, specifically, the pH value of the dissolution filtrate is adjusted to 6.9-7.1 by adopting an acidic solution. In the present invention, the concentration of the acidic solution is preferably 0.1mol/L, and the acidic solution preferably includes a hydrochloric acid solution, a sulfuric acid solution, or a nitric acid solution. The invention has no special requirements on the addition amount and the addition form of the acidic solution so as to obtain the target pH value. The pH value is preferably adjusted to 6.9-7.1, and more preferably to 7.0.
The invention provides a method for removing arsenic in heavy metal contaminated soil, which comprises the steps of firstly mixing a reinforcer, the heavy metal contaminated soil and water, and carrying out arsenic dissolution treatment on the heavy metal contaminated soil to obtain dissolution filtrate; and then adsorbing the dissolution filtrate by using an adsorbent. According to the invention, the enhancer is adopted to realize the dissolution of arsenic in the heavy metal contaminated soil, and the combination with the dissolved arsenic is realized by combining the adsorption effect of the subsequent adsorbent, so that the absorption and removal of arsenic are realized, the toxicity is reduced, and the problem of secondary pollution is avoided.
The following examples are provided to illustrate the method for removing arsenic from heavy metal contaminated soil according to the present invention, but they should not be construed as limiting the scope of the present invention.
The following examples and comparative examples were collected from As-contaminated rice fields (110.96 ° E, 29.35 ° N) in the gulf of king, cili county, hunan, and soil As contaminated in the rice fields mainly originated from the core region of the near-neighbor Shimen realgar mine, the collection depth was 0-20 cm from the topsoil plough layer, and the soil samples were naturally air-dried indoors and ground through a 2mm sieve for later use. The invention has no special requirements on the testing mode of the arsenic metal content, and the heavy metal content testing mode known by the technical personnel in the field can be adopted.
Example 1
According to NH4H2PO4The mass ratio of the rice to be treated to the rice soil is 75.67 g: 1kg of NH with a concentration of 0.05mol/L4H2PO4Mixing the water solution, and placing in an incubator at 30 ℃. Shaking at 150rpm for 16h, centrifuging at 3500r/min for 5min, separating soil and filtrate, and collecting filtrate.
The content of arsenic in the separated soil was measured to obtain the amount of arsenic eluted from the soil, and the results are shown in table 1.
Measuring the concentration of arsenic in the filtrate, and according to the mass of C-NZVI: mixing the filtrate with C-NZVI according to the volume ratio of 4g to 1L, oscillating for 24h to complete the adsorption of arsenic in the filtrate, and measuring the removal rate of arsenic in the adsorbed filtrate, wherein the results are shown in Table 1.
example 2
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 1 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 60 g:1 kg.
The amount of arsenic eluted from the soil, the concentration of arsenic in the filtrate after the enhanced elution, and the removal rate of arsenic from the filtrate were measured, and the results are shown in table 1.
Example 3
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 1 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 65 g:1 kg.
The amount of arsenic eluted from the soil, the concentration of arsenic in the filtrate after the enhanced elution, and the removal rate of arsenic from the filtrate were measured, and the results are shown in table 1.
Example 4
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 1 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 80 g:1 kg.
The amount of arsenic eluted from the soil, the concentration of arsenic in the filtrate after the enhanced elution, and the removal rate of arsenic from the filtrate were measured, and the results are shown in table 1.
Example 5
The soil to be treated was subjected to digestion and adsorption treatment in the manner of example 1, except that the C-NZVI adsorbent was replaced with iron oxide Fe2O3。
The amount of arsenic eluted from the soil, the concentration of arsenic in the filtrate after the enhanced elution, and the removal rate of arsenic from the filtrate were measured, and the results are shown in table 1.
TABLE 1 examples 1 to 5 soil dissolution effect and removal rate of arsenic in filtrate by adsorbent
Example 6
According to NH4H2PO4The mass ratio of the rice to be treated to the rice soil is 75.67 g: 1kg of NH with a concentration of 0.05mol/L4H2PO4and (3) fully mixing the aqueous solution, placing the aqueous solution in an incubator at 30 ℃, oscillating at the frequency of 150rpm for 16h, then carrying out centrifugal filtration at the rotation speed of 3500r/min for 5min, separating out soil and filtrate, and collecting the filtrate separated out for the first time.
According to (NH)4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 373.97 g: 1kg of (NH) was added to the treated soil4)2C2O4Aqueous solution of (NH)4)2C2O4The concentration of the aqueous solution is 0.2mol/l, the oscillation is carried out according to the frequency of 150rpm, the oscillation time is 16h, the rotation speed of centrifugal filtration is 3500r/min, the centrifugal time is 5min, the soil and the second filtrate are separated, and the second filtrate is collected.
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 2.
The arsenic concentration in the second filtrate was measured and the results are shown in table 2; and according to the mass of C-NZVI: mixing the filtrate with C-NZVI and the collected second-time dissolution filtrate according to the volume ratio of 4g to 1L, oscillating for 24h to complete the adsorption of arsenic in the second-time dissolution filtrate, and measuring the removal rate of arsenic in the filtrate, wherein the results are shown in Table 2.
Example 7
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 7 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 75.67 g:1 kg; (NH)4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 360 g:1 kg.
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 2.
The concentration of arsenic in the second filtrate was measured to complete the adsorption of arsenic in the second leaching filtrate, and the removal rate of arsenic in the filtrate was measured, with the results shown in table 2.
Example 8
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 7 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 75.67 g:1kg；(NH4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 380 g:1 kg.
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 2.
The concentration of arsenic in the second filtrate was measured, and after adsorption of arsenic in the second leaching filtrate was completed, the removal rate of arsenic in the filtrate was measured, and the results are shown in table 2.
Example 9
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 7 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 75.67 g:1 kg; (NH)4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 390 g:1 kg.
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 2.
The concentration of arsenic in the second filtrate was measured, and after adsorption of arsenic in the second leaching filtrate was completed, the removal rate of arsenic in the filtrate was measured, and the results are shown in table 2.
Example 10
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 7 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 75.67 g:1 kg; (NH)4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 373.97 g: 1kg, and replacing the C-NZVI adsorbent with iron oxide Fe2O3。
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 2.
The concentration of arsenic in the second filtrate was measured, and after adsorption of arsenic in the second leaching filtrate was completed, the removal rate of arsenic in the filtrate was measured, and the results are shown in table 2.
Table 2: examples 6 to 10 soil dissolution Effect and removal efficiency of arsenic in the second dissolution filtrate by the adsorbent
Example 11
According to NH4H2PO4The mass ratio of the rice to be treated to the rice soil is 75.67 g: 1kg of NH with a concentration of 0.05mol/L4H2PO4Mixing the water solution, and placing in an incubator at 30 ℃. Shaking at 150rpm for 16h, centrifuging at 3500r/min for 5min, separating soil and filtrate, and collecting filtrate.
According to (NH)4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 373.97 g: 1kg of (NH) was added to the treated soil4)2C2O4Aqueous solution of (NH)4)2C2O4The concentration of the water solution is 0.2mol/l, the oscillation is carried out according to the frequency of 150rpm, the oscillation time is 16h, the rotation speed of centrifugal filtration is 3500r/min, the centrifugation time is 5min, the soil and the second dissolution filtrate are separated, and the soil and the second dissolution filtrate are collected.
According to Na2SiO3The mass ratio of (a) to the initial pretreated rice soil was 213.9 g: 1kg of Na with a concentration of 1.75mol/L was added to the soil separated twice2SiO3Mixing the water solutions, placing in 30 deg.C incubator, and processing in dark. Shaking at 150rpm for 16h, centrifuging at 3500r/min for 5min, separating soil and third filtrate, and collecting the third filtrate.
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 3.
Mixing the first separated filtrate, the second filtrate and the third filtrate, and measuring the concentration of arsenic in the mixed filtrate, wherein the results are shown in table 3; and according to the mass of C-NZVI: volume of filtrate 3.5 g: the results of mixing C-NZVI with the collected mixed filtrate at a ratio of 1L, shaking the mixture for 24 hours to complete the adsorption of arsenic in the mixed filtrate, and measuring the removal rate of arsenic in the adsorbed filtrate are shown in Table 3.
Example 12
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 11 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 60 g:1 kg; (NH)4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 360 g:1 kg; na (Na)2SiO3The mass ratio of (a) to the initial pretreated rice soil is 200 g:1 kg.
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 3.
Mixing the first separated, second filtrate and third filtrate, and measuring the concentration of arsenic in the mixed filtrate, the results are shown in table 3; and according to the mass of C-NZVI: mixing C-NZVI with the collected mixed filtrate according to the volume ratio of the filtrate to 1g, oscillating for 24h to complete the adsorption of arsenic in the mixed filtrate, and measuring the removal rate of arsenic in the mixed filtrate, wherein the results are shown in Table 3.
Example 13
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 11 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 65 g:1 kg; (NH)4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 380 g:1 kg; na (Na)2SiO3The mass ratio of (a) to the initial pretreated rice soil is 220 g:1 kg.
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 3.
mixing the first separated filtrate, the second filtrate and the third filtrate, and measuring the concentration of arsenic in the mixed filtrate, wherein the results are shown in table 3; and according to the mass of C-NZVI: the volume of the filtrate was 4g to 1L, C-NZVI was mixed with the collected mixed filtrate, the mixture was shaken for 24 hours to complete the adsorption of arsenic in the mixed filtrate, and the removal rate of arsenic in the mixed filtrate was measured, and the results are shown in Table 3.
Example 14
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 11 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 80 g:1 kg; (NH)4)2C2O4The mass ratio of the pre-treated rice soil to the initial pre-treated rice soil is 390 g:1 kg; na (Na)2SiO3The mass ratio of (a) to the initial pretreated rice soil is 230 g:1 kg.
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 3.
Mixing the first separated filtrate, the second filtrate and the third filtrate, and measuring the concentration of arsenic in the mixed filtrate, wherein the results are shown in table 3; and according to the mass of C-NZVI: the volume of the filtrate was 1.5 g/L, C-NZVI was mixed with the collected mixed filtrate, the mixture was shaken for 24 hours to complete the adsorption of arsenic in the mixed filtrate, and the removal rate of arsenic in the mixed filtrate was measured, and the results are shown in Table 3.
Example 15
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 11 except that NH was added4H2PO4The mass ratio of the rice to be treated to the rice soil is 75.67 g:1 kg; (NH)4)2C2O4The mass ratio of the pre-treated paddy soil to the initial pre-treated paddy soil is 373.97g：1kg；Na2SiO3The mass ratio of (a) to the initial pretreated rice soil was 213.9 g: 1kg, and replacing the C-NZVI adsorbent with iron oxide Fe2O3。
The arsenic content in the finally separated soil was measured and compared with the arsenic content in the initially pretreated paddy soil to obtain the amount of arsenic eluted from the soil, and the results are shown in table 3.
Mixing the first separated filtrate, the second filtrate and the third filtrate, and measuring the concentration of arsenic in the mixed filtrate, wherein the results are shown in table 3; and according to Fe2O3The mass of (A): the volume of the filtrate is 2g to 1L, and Fe2O3The filtrate was mixed with the collected mixed filtrate, and the mixture was shaken for 24 hours to complete adsorption of arsenic in the mixed filtrate, and the removal rate of arsenic in the mixed filtrate was measured, and the results are shown in table 3.
TABLE 3 examples 11 to 15 soil dissolution effect and removal rate of arsenic in mixed filtrate by adsorbent
From the test results of examples 1 to 16 and tables 1 to 3, it is clear that the high-efficiency removal of the As load on the paddy soil can be realized by enhancing the dissolution of the dissolved paddy soil As through flooding; C-NZVI to NH4H2PO4The removal rate of water-soluble As (705-820 mu g/L) generated under the enhanced dissolution effect is not lower than 95 percent; the removal rate of the filtrate in the second dissolution mode is stabilized to be more than 91 percent, and the removal rate of C-NZVI to As in the filtrate in the third dissolution mode reaches to be more than 95 percent.
According to the invention, the soil with total arsenic content of 60.43mg/kg is subjected to dissolution treatment by stepwise dissolution, in the dissolution treatment process, the soil is dissolved by flooding, and the height of the soil surface polluted by water exceeding heavy metal is 2-5 cm. In the first step, 75.67g NH/kg soil was used4H2PO4Performing flooding dissolution on soil, wherein the concentration of water-soluble As in the rice soil in dissolution filtrate reaches 705.13-820.02 mug/L; the second step is carried out using 373.97g (NH) per kg of soil4)2C2O4Further carrying out dissolution treatment on the soil separated after the first dissolution, testing the concentration of arsenic in the dissolution filtrate of the second step, and increasing the dissolution concentration of arsenic in the dissolution filtrate of the two steps to 923.56-1157.39 [ mu ] g/L; the third step is to use 213.91g of Na per kg of soil2SiO3And (3) carrying out dissolution treatment on the soil separated by the second dissolution, wherein the dissolution concentration accumulation of arsenic in the dissolution filtrate obtained in the third step reaches 1291.15-1488.87 mug/L, and the total concentration (60.43mg/kg) of the accumulated dissolution concentration (16.56-19.02 mg/kg) of the As in the soil is 27% -31% of the total concentration (60.43mg/kg), namely the removal rate of the arsenic in the soil reaches 27-31%. The results show that the addition of the enhancer can effectively enhance the activated dissolution of the As in the flooded rice soil, which provides necessary conditions for the efficient ectopic removal of the As load in the rice soil.
Example 16
The soil to be treated was subjected to elution and adsorption treatment in the same manner as in example 1 except that NH was added4H2PO4Is replaced by (NH)4)2C2O4。
And measuring the concentration of arsenic in the filtrate to obtain the concentration of arsenic in the filtrate of 310 mug/L, completing the adsorption of arsenic in the filtrate, and measuring the concentration of arsenic in the filtrate after adsorption to obtain the removal rate of arsenic in the filtrate of 95.8%.
Example 17
According to Na2SiO3The mass ratio of the rice to be treated to the rice soil is 75.67 g: 1kg of Na with a concentration of 0.05mol/L2SiO3Mixing the water solutions, placing in 30 deg.C incubator, and processing in dark. Shaking at 150rpm for 16h, centrifuging at 3500r/min for 5min, separating soil and filtrate, and collecting filtrate.
Measuring the concentration of arsenic in the filtrate to obtain the concentration of arsenic in the filtrate of 360 mu g/L and the pH of 13.07, dividing the filtrate into three parts, respectively adopting hydrochloric acid solution with the concentration of 1mol/L to adjust the pH values of the collected filtrates to be 6.9, 7 and 7.1, and then according to the mass of C-NZVI: mixing the filtrate with C-NZVI according to the volume ratio of 4g to 1L, oscillating for 24.h to complete the adsorption of arsenic in the filtrate, and measuring the concentration of arsenic in the adsorbed filtrate to obtain the removal rates of 99.4%, 99.9% and 99.5%.
Comparative example 1
The rice soil was flooded in a soil-water ratio of 1:3(1g soil: 3mL water) and placed in an incubator at 30 ℃ under dark conditions, the amount of arsenic eluted from the soil was measured on day 6, and the concentration of arsenic in the elution filtrate was measured, and the results are shown in Table 4.
Comparative example 2
According to the weight ratio of 1g soil: adding 0.5mmol/L K into rice soil to be treated at a ratio of 3mL of treatment solution2HPO4The aqueous solution (2) was thoroughly mixed and placed in an incubator at 30 ℃ and protected from light, the amount of arsenic eluted from the soil was measured on day 6, and the concentration of arsenic in the eluted filtrate was measured, and the results are shown in Table 4.
Comparative example 3
According to the weight ratio of 1g soil: 3mL of the treatment solution, 0.5mmol/L of Na is added to the rice soil to be treated2SiO3The aqueous solution (2) was thoroughly mixed and placed in an incubator at 30 ℃ and protected from light, the amount of arsenic eluted from the soil was measured on day 6, and the concentration of arsenic in the eluted filtrate was measured, and the results are shown in Table 4.
Comparative example 4
According to the weight ratio of 1g soil: 3mL of the treatment solution, 0.5mmol/L of H is added to the rice soil to be treated3BO3The aqueous solution (2) was thoroughly mixed and placed in an incubator at 30 ℃ and protected from light, the amount of arsenic eluted from the soil was measured on day 6, and the concentration of arsenic in the eluted filtrate was measured, and the results are shown in Table 4.
Comparative example 5
According to the weight ratio of 1g soil: adding 0.5mmol/L CH into the rice soil to be treated at a ratio of 3mL of treatment solution3The COOH aqueous solution was thoroughly mixed and placed in a 30 ℃ incubator, protected from light, and the amount of arsenic eluted from the soil was measured on day 6, and the concentration of arsenic in the eluted filtrate was measured, and the results are shown in table 4.
TABLE 4 comparative examples 1 to 5 after the leaching treatment, the arsenic concentration in the leaching filtrate and the amount of arsenic eluted from the soil
As can be seen from comparison of tables 1 to 4, the adequate enhancer can sufficiently dissolve out arsenic in the heavy metal soil only under the condition of reasonable dosage.
Comparative example 6
The soil to be treated was treated in the manner of example 17, with the difference that, after obtaining the filtrate, the mass of C-NZVI was directly: mixing the filtrate with C-NZVI according to the volume ratio of 4g/L, oscillating for 24h to complete the adsorption of arsenic in the filtrate, and measuring the concentration of arsenic in the adsorbed filtrate to obtain the removal rate of almost 0.
From the measurement results of example 17 and comparative example 6, Na was found2SiO3The addition of (A) raises the original pH of the liquid phase of the rice to 13.07, thereby causing the removal rate of AsIII therein by C-NZVI to approach zero, mainly because AsIII is mainly in H under the pH condition2AsO3 -And HAsO3 2-In anionic form (pKa)1＝9.2， pKa212.1) with higher OH concentration-A large number of anion adsorption sites on the surface of the C-NZVI are occupied through coordination and complexation reaction, so that a remarkable competitive inhibition effect is generated on AsIII adsorption. However, when the pH of the liquid phase generated in the step is adjusted to 6.9-7.1 by HCl, the adsorption removal efficiency of C-NZVI on water-soluble As in the liquid phase is rapidly increased to 99%, which indicates that properly reducing the pH of the liquid phase reaction system plays an important role in improving the AsIII adsorption efficiency of C-NZVI.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (10)
1. A method for removing arsenic in heavy metal contaminated soil comprises the following specific steps:
(1) Mixing the reinforcer, the heavy metal contaminated soil and water, and then carrying out arsenic dissolution treatment on the heavy metal contaminated soil to obtain dissolution filtrate;
(2) Adsorbing the digestion filtrate by using an iron-based adsorbent;
The dissolution treatment is three-step dissolution, and the three-step dissolution comprises the following steps: mixing the heavy metal contaminated soil, water and a first portion of enhancer, and carrying out primary dissolution on the heavy metal contaminated soil to obtain primary dissolution filtrate and second heavy metal contaminated soil; mixing a second enhancer, water and second heavy metal contaminated soil, and performing second dissolution to obtain a second dissolution filtrate and third heavy metal contaminated soil; mixing a third enhancer, water and third heavy metal contaminated soil, and dissolving out for the third time; by NH4H2PO4The aqueous solution is used for dissolving out heavy metal polluted soil for the first time; by (NH)4)2C2O4The water solution is used for carrying out secondary dissolution on the second heavy metal contaminated soil; by using Na2SiO3The water solution of (2) is used for carrying out third dissolution on the third heavy metal contaminated soil;
The mass ratio of the first part of reinforcing agent to the second part of reinforcing agent to the third part of reinforcing agent is 1: 4.87-6: 2.82-3.38.
2. The removal method according to claim 1, wherein the arsenic elution treatment is an oscillation elution or a stirring elution; the frequency of the shaking elution and the stirring elution are independently 150 to 200 rpm.
3. The removal method according to claim 1, wherein the iron-based adsorbent in the step (2) is zero-valent iron or iron oxide.
4. The removal method according to claim 1, wherein the amount of the water is 2 to 5cm in height above the surface of the heavy metal-contaminated soil.
5. The removal method of claim 1, wherein the enhancer is a composition comprising NH4 +、H2PO4 -、HPO4 2-、C2O4 2-and SiO3 2-A compound or mixture of one or more ions.
6. The removal method according to claim 1 or 5, wherein the strengthening agent comprises NH4H2PO4、(NH4)2C2O4、Na2SiO3、KH2PO4、Na2C2O4And CaSiO3One or more of (a).
7. The removal method according to claim 6, wherein the mass of the enhancer is 60-700 mg/kg of the mass of the heavy metal contaminated soil.
8. The removal method according to claim 7, wherein when the strengthening agent comprises NH4H2PO4、(NH4)2C2O4And Na2SiO3When is in contact with the NH4H2PO4The mass of the heavy metal-contaminated soil is 60-80 mg/kg of the mass of the heavy metal-contaminated soil; said (NH)4)2C2O4The mass of the heavy metal-contaminated soil is 360-390 mg/kg of the mass of the heavy metal-contaminated soil; the Na is2SiO3The mass of the heavy metal-contaminated soil is 200-230 mg/kg of the mass of the heavy metal-contaminated soil.
9. The removing method according to claim 5, wherein when the reinforcing agent contains SiO3 2-And adjusting the pH value of the dissolution filtrate before adsorption, specifically, adjusting the pH value of the dissolution filtrate to 6.9-7.1 by using an acidic solution.
10. The removal method according to claim 1, wherein the mass to dissolution filtrate volume ratio of the adsorbent is 1 to 4g: 1L.
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| CN1705525A (en) * | 2002-10-24 | 2005-12-07 | 帝人纤维株式会社 | Method for clarifying soil |
| CN102974607A (en) * | 2012-12-21 | 2013-03-20 | 中国科学院地理科学与资源研究所 | Elution repairing device and repairing method of arsenic polluted soil and wastes |
| CN103990646A (en) * | 2014-04-25 | 2014-08-20 | 路域生态工程有限公司 | Leaching apparatus for arsenic-contaminated soil and treatment method for arsenic-contaminated soil |
| JP5748015B1 (en) * | 2014-04-03 | 2015-07-15 | 宇部興産株式会社 | Insolubilizer and insolubilization method |
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| WO2002043814A1 (en) * | 2000-11-28 | 2002-06-06 | Ada Technologies, Inc. | Improved method for fixating sludges and soils contaminated with mercury and other heavy metals |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1705525A (en) * | 2002-10-24 | 2005-12-07 | 帝人纤维株式会社 | Method for clarifying soil |
| CN102974607A (en) * | 2012-12-21 | 2013-03-20 | 中国科学院地理科学与资源研究所 | Elution repairing device and repairing method of arsenic polluted soil and wastes |
| JP5748015B1 (en) * | 2014-04-03 | 2015-07-15 | 宇部興産株式会社 | Insolubilizer and insolubilization method |
| CN103990646A (en) * | 2014-04-25 | 2014-08-20 | 路域生态工程有限公司 | Leaching apparatus for arsenic-contaminated soil and treatment method for arsenic-contaminated soil |
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